Impregnated activated carbon, such as, but not limited to, ASZM-TEDA (Activated Carbon, Impregnated with Copper, Silver, Zinc, Molybdenum, and/or Triethlyenediamine), is used as filter media in individual and collective protection systems used by the military. The high-surface area activated carbon possesses excellent adsorption capacity for physically adsorbing chemical warfare gases. Although the impregnated activated carbon provides excellent initial protection against vapors and acidic/acid-forming gases, the capacity of activated carbon degrades over time from exposure to contaminants, such as SO2 and water condensation. Mechanical integrity defect formation in the carbon filter, such as flow channeling or filter settling, can also impair the filtration performance.
Active carbon filter degradation detection and residual life prediction has been studied by many researchers. Hori et al. used a semiconductor gas sensor to detect breakthrough of organic vapors (Hori et al. 2003); Bernard et al. patented a method using fiber optic chemical sensor for indicating the end of service life of a respirator cartridge (Bernard et al. 2002); Rubel, et al. used electrochemical impedance spectroscopy to detect SO2 and humidity in impregnated active carbon (Rubel et al. 2009).
These methods provide approaches to detect specific chemical presence or sense chemical concentration in the carbon filters. However, current sensing technologies are lacking of the capability of detecting mechanical changes, such as carbon packing, settling flow channeling, etc. Furthermore, the sensors and related measurement device are cumbersome and often has high power requirement, which limited their use in respirator cartridges.
As such, a need exists for methods to detect the degradation of impregnated active carbon filters.